Specifications
Surface Treatments
Certifications
- ISO 9001 - 2015 Certified
- PED 2014/68/EC
- NACE MR0175/ISO 15156-2
- NORSOK M-650
- DFAR
- MERKBLATT AD 2000 W2/W7/W10
ASME B18.2.1 Hex Cap Screws
Precision-machined hex bolts with washer faces and chamfered points designed for high-strength mechanical and structural joint applications.
ASME B18.2.1 Hex Cap Screws, often referred to as finished hex bolts, are precision fasteners distinguished by a washer face under the head and a chamfered point on the unthreaded end. These features facilitate easier assembly, distribute load more evenly, and prevent damage to the mating surface during tightening. Unlike standard hex bolts, cap screws are manufactured to tighter tolerances regarding body diameter and head dimensions, making them suitable for precision machinery, automotive assemblies, and structural steel connections where alignment and fit are critical. They are typically used with nuts or threaded into tapped holes and are available in various material grades to meet specific tensile strength requirements. The ASME B18.2.1 standard governs their dimensional consistency, ensuring interchangeability and reliability across diverse industrial sectors.
ASME B18.2.1 Hex Cap Screws Dimensions (Inch)
| Nominal Size or Basic Product Diameter | Body Diameter, E | Width Across Flats, F | Width Across Corners, G | Head Height, H | Minimum Wrenching Height, J | Nominal Thread Length for Screw Lengths, LT | Transition Thread Length, Y | Maximum Total Runout of Bearing Surface FIM | ||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Max. | Min. | Basic | Max. | Min. | Max. | Min. | Basic | Max. | Min. | 6 in. and Shorter | Over 6 in. | |||||
| 1/4 | 0.2500 | 0.2500 | 0.2450 | 7/16 | 0.438 | 0.428 | 0.505 | 0.488 | 5/32 | 0.163 | 0.150 | 0.106 | 0.750 | 1.000 | 0.250 | 0.010 |
| 5/16 | 0.3125 | 0.3125 | 0.3065 | 1/2 | 0.500 | 0.489 | 0.577 | 0.557 | 13/64 | 0.211 | 0.195 | 0.140 | 0.875 | 1.125 | 0.278 | 0.011 |
| 3/8 | 0.3750 | 0.3750 | 0.3690 | 9/16 | 0.562 | 0.551 | 0.650 | 0.628 | 15/64 | 0.243 | 0.226 | 0.160 | 1.000 | 1.250 | 0.312 | 0.012 |
| 7/16 | 0.4375 | 0.4375 | 0.4305 | 5/8 | 0.625 | 0.612 | 0.722 | 0.698 | 9/32 | 0.291 | 0.272 | 0.195 | 1.125 | 1.375 | 0.357 | 0.013 |
| 1/2 | 0.5000 | 0.5000 | 0.4930 | 3/4 | 0.750 | 0.736 | 0.866 | 0.840 | 5/16 | 0.323 | 0.302 | 0.215 | 1.250 | 1.500 | 0.385 | 0.014 |
| 9/16 | 0.5625 | 0.5625 | 0.5545 | 13/16 | 0.812 | 0.798 | 0.938 | 0.910 | 23/64 | 0.371 | 0.348 | 0.250 | 1.375 | 1.625 | 0.417 | 0.015 |
| 5/8 | 0.6250 | 0.6250 | 0.6170 | 15/16 | 0.938 | 0.922 | 1.083 | 1.051 | 25/64 | 0.403 | 0.378 | 0.269 | 1.500 | 1.750 | 0.455 | 0.017 |
| 3/4 | 0.7500 | 0.7500 | 0.7410 | 1 1/8 | 1.125 | 1.100 | 1.299 | 1.254 | 15/32 | 0.483 | 0.455 | 0.324 | 1.750 | 2.000 | 0.500 | 0.020 |
| 7/8 | 0.8750 | 0.8750 | 0.8660 | 1 5/16 | 1.312 | 1.285 | 1.516 | 1.465 | 35/64 | 0.563 | 0.531 | 0.378 | 2.000 | 2.250 | 0.556 | 0.023 |
| 1 | 1.0000 | 1.0000 | 0.9900 | 1 1/2 | 1.500 | 1.469 | 1.732 | 1.675 | 39/64 | 0.627 | 0.591 | 0.416 | 2.250 | 2.500 | 0.625 | 0.026 |
| 1 1/8 | 1.1250 | 1.1250 | 1.1140 | 1 11/16 | 1.688 | 1.631 | 1.949 | 1.859 | 11/16 | 0.718 | 0.658 | 0.461 | 2.500 | 2.750 | 0.714 | 0.029 |
| 1 1/4 | 1.2500 | 1.2500 | 1.2390 | 1 7/8 | 1.875 | 1.812 | 2.165 | 2.066 | 25/32 | 0.813 | 0.749 | 0.530 | 2.750 | 3.000 | 0.714 | 0.033 |
| 1 3/8 | 1.3750 | 1.3750 | 1.3630 | 2 1/16 | 2.062 | 1.994 | 2.382 | 2.273 | 27/32 | 0.878 | 0.810 | 0.569 | 3.000 | 3.250 | 0.833 | 0.036 |
| 1 1/2 | 1.5000 | 1.5000 | 1.4880 | 2 1/4 | 2.250 | 2.175 | 2.598 | 2.480 | 15/16 | 0.974 | 0.902 | 0.640 | 3.250 | 3.500 | 0.833 | 0.039 |
| 1 5/8 | 1.6250 | 1.6250 | 1.6130 | 2 7/16 | 2.438 | 2.356 | 2.815 | 2.686 | 1 | 1.038 | 0.962 | 0.694 | 3.500 | 3.750 | 0.909 | 0.043 |
| 1 3/4 | 1.7500 | 1.7500 | 1.7380 | 2 5/8 | 2.625 | 2.538 | 3.031 | 2.893 | 1 3/32 | 1.134 | 1.054 | 0.748 | 3.750 | 4.000 | 1.000 | 0.046 |
| 1 7/8 | 1.8750 | 1.8750 | 1.8630 | 2 13/16 | 2.812 | 2.719 | 3.248 | 3.099 | 1 5/32 | 1.198 | 1.114 | 0.802 | 4.000 | 4.250 | 1.000 | 0.049 |
| 2 | 2.0000 | 2.0000 | 1.9880 | 3 | 3.000 | 2.900 | 3.464 | 3.306 | 1 7/32 | 1.263 | 1.175 | 0.825 | 4.250 | 4.500 | 1.111 | 0.052 |
| 2 1/4 | 2.2500 | 2.2500 | 2.2380 | 3 3/8 | 3.375 | 3.262 | 3.897 | 3.719 | 1 3/8 | 1.423 | 1.327 | 0.933 | ... | 5.000 | 1.111 | 0.059 |
| 2 1/2 | 2.5000 | 2.5000 | 2.4880 | 3 3/4 | 3.750 | 3.625 | 4.330 | 4.133 | 1 17/32 | 1.583 | 1.479 | 1.042 | ... | 5.500 | 1.250 | 0.065 |
| 2 3/4 | 2.7500 | 2.7500 | 2.7380 | 4 1/8 | 4.125 | 3.988 | 4.763 | 4.546 | 1 11/16 | 1.744 | 1.632 | 1.151 | ... | 6.000 | 1.250 | 0.072 |
| 3 | 3.0000 | 3.0000 | 2.9880 | 4 1/2 | 4.500 | 4.350 | 5.196 | 4.959 | 1 7/8 | 1.935 | 1.815 | 1.290 | ... | 6.500 | 1.250 | 0.079 |
ASME B18.2.1 Hex Cap Screws Length Tolerance (Inch)
| Nominal Length | Nominal Size | |||||
|---|---|---|---|---|---|---|
| 1/4 to 3/8 | 7/16 and 1/2 | 9/16 to 3/4 | 7/8 and 1 | 1 1/8 to 1 1/2 | Over 1 1/2 | |
| Up to 1 in., incl. | +0.00 0.03 |
+0.00 0.03 |
+0.00 0.03 |
... | ... | ... |
| Over 1 in. to 2 1/2 in., incl. | +0.00 0.04 |
+0.00 0.06 |
+0.00 0.08 |
+0.00 0.10 |
+0.00 0.12 |
+0.00 0.18 |
| Over 2 1/2 in. to 4 in., incl. | +0.00 0.06 |
+0.00 0.08 |
+0.00 0.10 |
+0.00 0.14 |
+0.00 0.16 |
+0.00 0.20 |
| Over 4 in. to 6 in., incl. | +0.00 0.10 |
+0.00 0.10 |
+0.00 0.10 |
+0.00 0.16 |
+0.00 0.18 |
+0.00 0.22 |
| Longer than 6 in. | +0.00 0.18 |
+0.00 0.18 |
+0.00 0.18 |
+0.00 0.20 |
+0.00 0.22 |
+0.00 0.24 |
Frequently Asked Questions
- What does ASME B18.2.1 hex cap screws cover?
- ASME B18.2.1 is the inch dimensional standard for hex cap screws. It defines head dimensions, body diameter, thread length, total length, drive recess, and tolerances so any compliant hex cap screws interchanges with standard nuts, washers and wrenches across manufacturers.
- What size range is available for hex cap screws under ASME B18.2.1?
- hex cap screws under ASME B18.2.1 covers 1/4 in to 1 1/2 in nominal diameter. TorqBolt manufactures the full range in ASTM A193 Grades B7, B7M, B8, B8M and the full ASTM A320 cryogenic counterpart on customer specification.
- What is the metric/inch counterpart of ASME B18.2.1 hex cap screws?
- The companion specification for hex cap screws is ASME B18.2.3 metric series. Both standards share equivalent functional dimensions but use the corresponding measurement system (inch vs metric ISO M-series).
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